Closed end type coiled spring with reduced initial deflection

ABSTRACT

In a coil spring of closed-end type, the coil spring is characterized in that a coupler is fixedly mounted between: an outer peripheral surface of a terminal convolution of a coil element rod; and, an outer peripheral surface of a subsequent convolution subsequent to the terminal convolution of the coil spring of closed-end type, whereby an amount of initial deflection is decreased.

TECHNICAL FIELD

The present invention relates to a coil spring used in a buffer springand like components of an automobile.

BACKGROUND ART

In order to improve an automobile and a bicycle in riding comfort inresponse to a road condition, a large number of inventions have beendisclosed with respect to a coil spring for supporting a vehicle body.For example, in a coil spring described in both Japanese Utility Modelapplication Laid-open No. Sho 56-20140 and Japanese Patent PublicationNo. Hei 2-22252, an elastic spacer is mounted in an intermediate portionof a coil element rod of the coil spring in order to change a coilconstant in response to a road condition.

In a coil spring described in Japanese Utility Model applicationLaid-open No. Sho 57-113739, a coiled spacer provided with anappropriate number of convolutions is inserted into a proximal terminalportion of the coil spring, so that the number of effective or activeconvolutions of the coil spring is changed so as to change the coilspring in its coil constant.

Further, a coil spring described in Japanese Patent applicationLaid-open No. Hei 6-42563 relates to a wearing washer for preventing thecoil spring from inclining due to its buckling when the coil spring isof an open-end type.

In contrast with these coil springs, the present invention improves acoil spring in spring properties by decreasing an amount of initialdeflection, wherein the initial deflection is a problem inherent in acoil spring of a closed-end type as described later.

Coil springs used in a buffer spring and like components of anautomobile are classified into: a coil spring of closed-end type asshown in FIG. 3( a), wherein a terminal portion of the coil spring issubjected to a flattening process; and, a coil spring of open-end typeas shown in FIG. 3( b), wherein a terminal portion of the coil spring isconstructed of a part of an active convolution of the coil spring.

In the case of the coil spring of open-end type shown in FIG. 3( b),when a compression force is applied to the coil spring by using a flatwasher, an oblique force which is obliquely directed with respect to acoil axis of the coil spring is developed to have the coil springinclined under the influence of its buckling caused by such obliqueforce.

Consequently, this type of the coil spring is disadvantageous in that itis necessary for the coil spring to use a special washer such as onedisclosed in the Japanese Patent application Laid-open No. Hei 6-42563.In contrast with this, in the case of the coil spring of closed-end typeas shown in FIG. 3( a), even when a flat washer is used, it is possiblefor the flat washer to apply a force uniformly to the coil spring inaxial direction thereof without using any special washer. Consequently,in this respect, the coil spring of such closed-end type isadvantageous.

In the case where a compression force is applied to the coil spring:when the coil spring is of the open-end type, as shown in dotted line ofFIG. 4( a), a plot of the coil spring of the open-end type forms astraight line from its starting point in a load-deflection diagram ofFIG. 4( a). As for the spring constant too, as shown in dotted line ofFIG. 4( b), a plot of the coil spring of the open-end type forms astraight line from its starting point in a coil spring-deflectiondiagram of FIG. 4( b). In contrast with this, in the case of the coilspring of closed-end type, as shown in solid line of FIG. 4( a): aterminal portion of the coil element rod of the coil spring is initiallydeflected under a relatively light load since such terminal portion ofthe coil spring of the closed-end type is smaller in cross-sectionalarea than any one of active convolution portions of the same coilspring; and, after that, a plot of the coil spring of the closed-endtype reaches its predetermined consistent form in the load-deflectiondiagram of FIG. 4( a). As for its spring constant, as shown in solidline of FIG. 4( b), a plot of the coil spring of the closed-end typegradually increases from its stating point, and reaches its consistentvalue at a completion point of its creeping. In this respect, the coilspring of the closed-end type is disadvantageous. In the presentinvention, such initial deflection occurring in the coil spring of theclosed-end type under the relatively light load is hereinafter referredto as “initial deflection”.

In order to avoid the above-mentioned disadvantage inherent in the coilspring of the closed-end type, it is considered that a preliminary loadis applied to the coil spring in installation to preliminarily removethe initial deflection of the coil spring from the coil spring'sinstallation height. However, in this method, since the coil spring issubstantially decreased in coil height in installation, it is notpossible to carry out this method in some application cases. Due tothis, a need exists in the art for the coil spring of the closed-endtype, which spring is substantially released from a problem of theinitial deflection by using a flat washer.

SUMMARY OF THE INVENTION

Consequently, it is an object of the present invention to solve theabove problem by providing a coil spring of closed-end type, wherein:the coil spring of the closed-end type is decreased in initialdeflection as is in the case of a coil spring of open-end type.

In order to accomplish the above object, the coil spring of theclosed-end type decreased in initial deflection according to the presentinvention is characterized in that a coupler is fixedly mounted between:an outer peripheral surface of a terminal portion of a coil element rodof the coil spring; and, an outer peripheral surface of a convolution ofthe coil spring, which convolution is subsequent to the terminal portionof the coil element rod.

In other words, in the coil spring of the closed-end type of the presentinvention: in order to prevent occurrence of the initial deflectionwhich is caused by the fact that the terminal portion of the coil springof the closed-end type is smaller in cross-sectional area than a normalconvolution portion of the coil spring and is therefore initiallydeflected under a relatively light load smaller than a given load, aforce applied to the terminal portion of the coil spring is transmittedto the subsequent convolution of the coil spring by using the coupler,so that the amount of such initial deflection of the coil spring isdecreased.

As a result of this, a load-deflection plot and a plot of springconstant of the coil spring of the closed-end type of the presentinvention each of which plots assumes a shape shown in FIG. 5. In otherwords, in the coil spring of the present invention, although a slightamount of the initial deflection initially appears as shown in thedrawings, such a slight amount of the initial deflection of the coilspring of the present invention is much smaller than the correspondinginitial deflection of the conventional coil spring of the closed-endtype (see FIG. 4). Consequently, it is possible for the coil spring ofthe present invention to considerably decrease the amount of the initialdeflection thereof. This makes it possible for the coil spring of thepresent invention to obtain substantially the same springcharacteristics as that of the coil spring of open-end type. Further, itis possible for the coil spring of the present invention to use a flatwasher as a wearing member for the coil spring. As a result, it ispossible for the coil spring of the present invention to reduce itsmanufacturing cost.

In contrast with the coil spring of the known invention described in theJapanese Utility Model application Laid-open No. Sho57-113739 in whichthe spacer is inserted into or removed from the coil spring so as tochange the number of effective or active convolutions of the coilspring, the present invention has the coupler of its coil spring fixedlymounted on the coil spring at the beginning of its installation in orderto keep a spring constant of the coil spring at a consistent value fromthe beginning of application of a compression force to the coil spring.

The coupler is preferably made of an elastic material. Further,preferably this coupler is made of an elastic material, which ismoderate in both hardness and elasticity so as not to damage a coilelement rod of the coil spring. Plastics, aluminum alloys, copper alloysand like materials can be used as the material of the coupler. As for amethod for fixedly mounting the coupler on the coil spring, it ispossible to bond the coupler to the coil spring with the use of anadhesive. Further, it is also possible to fixedly hold the coupler inthe coil spring with the use of resiliency of the coil spring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the coil spring decreased in its initialdeflection according to an embodiment of the present invention;

FIG. 2 is a perspective view illustrating an example of the coupler ofthe present invention;

FIG. 3 is a view describing both the coil spring of the closed-end typeand that of the open-end type;

FIG. 4 is a view illustrating the initial deflection of the coil springof the conventional closed-end type;

FIG. 5 is a view showing a load-deflection/spring constant diagram ofthe coil spring of the present invention when the spring is compressed;and,

FIG. 6 is a view showing the compression test values of the embodimentof the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

1 a coil spring of closed-end type; 2 a coil element rod; and, 3 acoupler.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

An embodiment of the present invention, which embodiment is illustratedin the drawings, will be hereinbelow described in a concrete manner.FIG. 1 is a perspective view of a coil spring of closed-end typeaccording to an embodiment of the present invention. FIG. 2 is aperspective view describing an example of a coupler of the presentinvention.

In FIG. 1, a coil spring of closed-end type of the present invention isconstructed of: a coil element rod 2 having each of its opposite coilterminal portions subjected to a surface-flattening process; and, acoupler 3 fixedly mounted on each of the opposite terminal portions 2 aof the coil element rod 2, which terminal portions 2 a are disposed inthe vicinities of opposite ends of the coil element rod 2 (in FIG. 1:only one of the opposite ends of the coil element rod 2 is illustrated;and, the other is not omitted in the drawing.).

As shown in detail in FIG. 2, an example of the coupler 3 of the presentinvention is constructed of a block which is provided with: a groove 3 ahaving a bottom radius, which radius permits the terminal portion 2 a ofthe coil element rod 2 to be steadily inserted into the groove 3 a; and,a groove 3 b provided in a rear surface oppositely disposed from thegroove 3 a in the block, wherein the groove 3 b of the block has abottom radius permitting the block to steadily mount on an outerperipheral surface of a convolution of the coil element rod in a raidingmanner, which convolution is disposed axially subsequent to the terminalportion (or convolution) 2 a of the coil element rod 2. This makes itpossible for the block to keep consistent a clearance between theterminal portion (or convolution) 2 a of the coil element rod 2 and thecorresponding outer peripheral surface of the axially subsequentconvolution of the coil element rod 2 when the coil spring of thepresent invention is compressed. Preferably, this block is made of asuitable elastic material having a moderate hardness so as not to damagethe coil element rod. Due to this, the block may be made of plastics andsoft metals both low in hardness. As for a method for fixedly mountingthe coupler on the coil spring of closed-end type of the presentinvention: although it is preferable to have at least one of the grooves3 a, 3 b of the coupler 3 is bonded to the coil element rod with the useof an adhesive, it is also possible to fixedly mount the block by aresiliency of the coil spring itself without using any adhesive.

Although the coupler 3 assumes a saddle-backed shape in the embodimentof the present invention so as to permit the coupler 3 to ride on thecoil element rod 2 of the coil spring, it is also possible for thecoupler 3 to have a through-hole permitting the coil element rod 2 of hecoil spring to pass through such through-hole of the coupler 3, and alsopossible for the coupler 3 to assume any other suitable shape in placeof the groove 3 b of the block.

Now, the coil spring of the present invention having the aboveconstruction will be described in operation. When the coil spring issubjected to a compression force: in case of a coil spring of aconventional closed-end type not provided with any coupler, since aterminal portion 2 a of such conventional closed-end type of coil springis smaller in cross-sectional area than any other convolution portion ofthe same coil spring, so that the terminal portion 2 a of suchconventional closed-end type of coil spring is initially deflected andbrought into contact with an outer peripheral surface of the subsequentconvolution of the coil spring to make it possible for the coil springto reach its consistent spring constant. Due to this, as shown in FIG. 4described above, the initial deflection is developed in the conventionalclosed-end type of coil spring.

In contrast with this, in case of the coil spring of the presentinvention: when the coil spring is subjected to a compression force, thecompression force applied to the terminal portion 2 a of the coilelement rod is transmitted to the subsequent convolution through thecoupler 3, so that, as shown in FIG. 5, the terminal portion 2 a of thecoil element rod is substantially not deflected, which makes it possiblefor the coil spring of the present invention employing the coupler 3 tokeep consistent its spring constant from substantially the beginning ofits compression process. As shown in FIG. 5, since the initialdeflection can be practically neglected in the coil spring of thepresent invention, it is possible for the coil spring of such closed-endtype of the present invention to obtain substantially the same springcharacteristics as that of the coil spring of open-end type.

As an example, a coil spring of closed-end type having mechanicalproperties shown in FIG. 1 were subjected to a series of compressiontests in two modes one of which corresponding to the coil spring of thepresent invention; and, the other corresponds to the conventional coilspring which is not provided with any coupler. The coupler was made ofmaterial called “Derlin”.

TABLE 1 Mechanical Properties of the Coil Spring thus tested Steel GradeSAE 9254 Tensile Strength (N/mm²) 1.991 Spring Constant (Kg f/mm) 8.0Coil Element Rod Diameter (mm) 11.80 Coil's Outer Diameter (mm) 88.6Total Number of Convolutions 6.85 Free Height (mm) 203.0

The results of the compression tests are shown in FIG. 6. As is clearfrom the drawing, in the conventional coil spring which is not providedwith any coupler: the initial deflection thereof was measured until thecoil height of the coil spring reached a value of 185 mm. In contrastwith this, in the coil spring of the present invention: when the coilspring having a fee height was compressed by an amount of 3 mm andreached a coil height of 200 mm, the coil spring showed its consistentspring constant. In other words, the coil spring, which is practicallyand substantially free from the initial deflection, was obtained.

As described above, in the coil spring of closed-end type of the presentinvention decreased in its initial deflection, the elastic couplerfixedly mounted between: the outer peripheral surface of the terminalconvolution of the coil element rod; and, the outer peripheral surfaceof the subsequent convolution of the same coil element rod, may transmitthe compression force applied to the terminal convolution of the coilelement rod to the subsequent convolution of the same coil element rod.Consequently, it is possible for the coil spring of the presentinvention to prevent the initial deflection from being developed duringits compression process. The initial deflection is a problem inherent inthe closed-end type of the conventional coil spring, because: theconventional coil spring of closed-end type has its coil terminalportion more decreased in cross-sectional area than any other portion ofthe coil spring in construction; and, is therefore deflected first evenwhen subjected to a smaller force than a given load of the coil spring.

Due to this, it is possible for the coil spring of the presentinvention, which uses the flat washers but not uses any special washer,to realize substantially the same spring characteristics as that of thecoil spring of open-end type provided with the special washers.

Disclosed in the Japanese Utility Model application Laid-open No. Sho57-113739 is a conventional coil spring of a known invention. This typeof conventional coil spring uses a spacer which is detachably insertedbetween selected adjacent ones of active convolutions of the coil springin order to change the number of its effective or active convolutions tochange a spring constant of the coil spring. In contrast with this, itis an object of the coil spring of the present invention to keepsubstantially consistent its spring constant from the beginning ofapplication of a given load to the coil spring by fixedly mounting thecoupler on the terminal portion of the coil element rod in thevicinities of the opposite end of the coil spring.

As for the coupler, preferably the coupler is provided with a moderatehardness and elasticity so as to prevent the coil element rod of thecoil spring from being damaged by the coupler. As for a method forfixedly mounting the coupler on the coil spring, it is possible toemploy any suitable method, for example such as: a bonding method inwhich the coupler is bonded to the terminal portion or convolution ofthe coil spring through a suitable adhesive applied to the terminalportion of the coil spring; and, a mechanical method in which thecoupler is fixedly mounted on the terminal portion or convolution of thecoil spring under the influence of a resilient force exerted by the coilspring.

POSSIBILITY IN INDUSTRIAL USE

As described above, in the coil spring of closed-end type of the presentinvention is decreased in initial deflection: in contrast with the coilspring of open-end type using the special washers, any special washer isnot required in the coil spring of the present invention; and, in placeof such special washer, a flat washer is used in the coil spring of thepresent invention. Due to this, it is possible for the coil spring ofthe present invention to realize substantially the same springcharacteristics as that of the coil spring of open-end type. As aresult, it is possible for the present invention to increase theapplication field of the coil spring of closed-end type according to thepresent invention.

1. In a coil spring of closed-end type, said coil spring ischaracterized in that a coupler, having a length less than a quarter ofa circle of the coil, is fixedly mounted between: an outer peripheralsurface of a terminal convolution of a coil element rod of the coilspring of closed-end type, said terminal convolution being partiallyflattened in cross section through a flattening process; and an outerperipheral surface of a subsequent convolution subsequent to saidterminal convolution of the coil spring of closed-end type, so that saidcoupler is brought into close contact with said outer peripheral surfaceof each of said terminal convolution and said subsequent convolution ofthe coil spring of closed-end type, whereby an amount of initialdeflection of the coil spring of closed-end type is decreased when thecoupler is compressed between the outer peripheral surface of saidterminal convolution and the outer peripheral surface of said subsequentconvolution, wherein said coupler is fixedly held between the terminalconvolution and the subsequent convolution of the coil element rod ofthe coil spring in an uncompressed state of the coil spring without agap between the outer peripheral surface of the terminal convolution anda first surface of the coupler and without a gap between the outerperipheral surface of the subsequent convolution and a second surface ofthe coupler.
 2. The coil spring of closed-end type decreased in theamount of initial deflection as set forth in claim 1, wherein saidcoupler is made of an elastic material.
 3. The coil spring of closed-endtype in the amount of initial deflection as set forth in claim 1,wherein the first surface and second surface of the coupler are fixedlyheld in contact with the outer peripheral surface of the terminalconvolution and the outer peripheral surface of the subsequentconvolution, respectively, by an adhesive.